In the fiber optical communication technology optical fiber ribbons, i.e. optical fibers, which by an exterior polymer sleeve are kept together to form a flat fiber package having a plurality of optical fibers extending in parallel, are more and more used. Typically a fiber ribbon can contain 4, 6, 8 or 12 individual fibers. When splicing such fiber ribbons to each other in a secure way, preferably welding can be used. Then, with the growing use of optical communication fibers, devices are required which can be used in the field. Such a welding device should among other things have a good shielding of the region around the splicing location, in which the very electrical arc is formed at the ends of the optical fibers, so that an operator of the welding device is well protected. A shielding would also protect this area against contamination from the surroundings. Furthermore, in order to obtain sufficiently good splices of two fiber ribbons a number of different conditions must be fulfilled, such as that the individual optical fibers in the opposite ends of two fiber ribbons are well aligned with each other, that the alignment can be checked immediately before the welding operation and that the alignment then can possibly be corrected. Also, a background illumination of the fiber ends to be spliced to each other should be provided in order to obtain pictures for checking the positions of opposite fiber ends.
U.S. Pat. No. 5,524,163, which corresponds to the published European patent application No. 0 720 032, discloses a device and a method for splicing optical fibers. The device comprises a microscope unit, a light emitting diode holder placed above the fibers and a cover enclosing the light emitting diode retainer. The microscope unit consists of a housing, three microscopes, a shutter unit, two mirrors and a CCD-sensor. The light emitting diode retainer, which comprises three light emitting diodes, is mounted to swing about the same shaft as the cover and is locked in a swung-down position by means of a magnet. A background illumination is obtained from the light emitting diodes directing light from above to the welding location. The light from the welding location is deflected by mirrors to reach a photodetector.
U.S. Pat. No. 4,914,797 and the published British application No. 20 052 786, which corresponds to German patent No. 30 19 425, disclose welding devices comprising a housing which is or can be mounted to swing. This British patent application, the published German patent application No. 32 45 229 and the published European patent application No. 0 494 809 disclose welding devices having different types of optical detection devices comprising mirrors among other things.
The published International patent application WO 96/27811 discloses an illumination of the welding location comprising a light source located under the horizontal plane through the welding location, the light from the light source being deflected by two mirrors placed in a lid of the device.
The cited U.S. Pat. No. 5,524,163, U.S. Pat. No. 5,046,813, the Japanese patent application No. 59-38 718 and the German patent No. 41 23 227 disclose hold-down mechanisms for optical fibers provided with springs and/or magnets.